Control of the moisture content (dew point) within a reaction vessel is an important consideration, particularly in processes for the decarburization and controlled oxidation of steel. Water vapor is an effective decarburizing agent when present in controlled amounts. If insufficient water vapor is present, the process rate decreases below acceptable limits, thereby adding to the cost and time of the decarburizing operation. If excessive water vapor is present, scaling will result causing a slow down of the process.
There have been efforts to control the moisture content within a reaction vessel. For example, H. N. Ipsen, U.S. Pat. No. 2,815,305, discloses a process in which gas is continuously withdrawn from a furnace and the dew point measured. If there is an unacceptable deviation in the dew point, then the composition of the gas admitted to the furnace is changed by the use of natural gas as a regulating medium.
F. W. Beall, U.S. Pat. No. 3,127,289, discloses a method of decarburizing steel in which the atmosphere in the annealing furnace is controlled by maintaining a desired H.sub.2 /H.sub.2 O equilibrium in the exit gas. The hydrogen content and/or the dew point of the incoming gas is varied while the equilibrium in the exit gas is maintained at a constant rate.
Richard M. Hamner et al., U.S. Pat. No. 4,909,436, discloses an apparatus for humidifying gases wherein a primary stream of gas of a selected pressure passes through a tube coupled to a device having a constriction therein. The constriction generates a downstream low pressure region. A controllable source of a secondary gas is operatively linked to the low pressure region. A dew point sensor is coupled to the tube downstream of the low pressure region and detects the dew point of the mixture. This dew point indication is used to manually regulate the pressure of the primary gas and the flow of secondary gas to achieve the desired dew point of the mixture. The dew point is therefore adjusted manually by moderating the temperature of the reaction vessel.
These efforts at controlling the dew point within a reaction vessel suffer from one or more drawbacks. In particular, the dew point is controlled by the injection of water vapor (steam) into the reaction vessel. Because steam is a gas, it is compressible and therefore more difficult to control. In addition, the system requires additional energy to generate the steam and greater cost because the steam is generated in a separate vessel.
The manual adjustment of the dew point is also disadvantageous because it is less accurate and more labor intensive than desirable for many applications.
It would therefore be of significant benefit to have an automated process in which a variable amount of liquid water is fed into the reaction vessel with the capability of automatically adjusting the water flow based on the input received from a dew point analyzer.